1. Field of the Invention
The present invention relates to an image reading apparatus which is configured to read an image from a manuscript on a contact glass by an image sensor contained in a carriage.
2. Description of the Related Art
Conventionally, as image reading apparatuses, so-called flatbed type image reading apparatuses have been known. Such an image reading apparatus has a contact glass at the upper surface of its main body for setting a manuscript. The image reading apparatus is configured to read an image of the manuscript set on the contact glass by an image sensor provided inside the main body. Then, the image sensor is installed on a carriage which is installed to be slidable on a rail provided inside the min body. The image sensor is configured to slide along the rail together with the carriage when reading the image of the manuscript.
As a configuration of such image reading apparatus, it is known that the image sensor has a longitudinal dimension in a main scanning direction and is placed on the carriage which is slidable along a guide shaft. Then, the image reading apparatus is configured to read an image of the manuscript set on the contact glass while sliding the image sensor, which is installed on the carriage, along the guide shaft.
In the abovementioned image reading apparatus, the carriage has a bearing on its lower surface in the central portion in the longitudinal direction. The bearing strides over the guide shaft from above to fit the guide shaft thereinto. By letting the bearing fit the guide shaft thereinto from above, the carriage is installed to the guide shaft to be slidable along the guide shaft.
Here, the bearing is formed on the lower surface of the carriage in the central portion in the longitudinal direction. Therefore, the carriage is supported by one point in the longitudinal direction of the carriage, namely the central portion at which the bearing is formed. Hence, the carriage is installed to the guide shaft swingably about the central portion in the longitudinal direction.
Then, the carriage is formed to have an open top box-like shape in which an upper surface on the contact glass side is open. The lower surface of the carriage is formed to have a uniform flat surface extending almost straight. Therefore, if the carriage swings about the central portion in the longitudinal direction, then one end portion of the carriage in the longitudinal direction moves up toward the contact glass, while the other end portion moves downward below the guide shaft.
When the carriage is installed to the guide shaft in the above manner, inevitably, the carriage swings with the guide shaft and the bearing being a center. Therefore, the abovementioned image reading apparatus needs to secure a space occupied by the carriage when the carriage swings, which becomes an obstacle to facilitating miniaturization of the image reading apparatus.
Further, in the image reading apparatus, the distance between the manuscript on the contact glass and the reading surface of the image sensor exerts an influence on the reading quality of the image reading apparatus. Therefore, even when the carriage has swung with the central portion in the longitudinal direction being a center, it is still necessary to maintain the reading surface of the image sensor installed to the carriage parallel to the contact glass.